a. Field of the Invention
The invention relates to in-situ anchors for use primarily in static structures. More particularly, the invention relates to a threaded anchor to be used in a blind hole in hard materials.
b. Prior Art
Previously, others have devised anchors which secure bolts in materials by means of internal threads. Some such anchors are held in place by outward expansion of at least a portion of the anchor. For example, in U.S. Pat. No. 3,171,321 granted Mar. 2, 1965, A. Fischer teaches an anchor for a blind hole which is longitudinally split at the inward end, but with the inward end otherwise solid. A screw which is driven into the anchor forces the split portion outwardly and into firm contact with walls of the hole in which the anchor is placed. The anchor material is plastic and undergoes some compression against the wall, holding the screw in place.
In U.S. Pat. No. 4,044,647 granted Aug. 30, 1970 to K. Takahashi an anchor is disclosed which is internally threaded and having split sides at the inward end of the anchor. The bottom of the anchor is partially closed, but having a central conical opening communicating with the longitudinal slit. A spreading tool is carried by the anchor and on insertion of the anchor into a hole the spreading tool is carried forward and pushed into the conical opening, thereby spreading the inward end of the anchor, securing it in position.
In U.S. Pat. No. 4,135,432 granted Jan. 23, 1979 to R. Schalge and G. Neos there is a disclosure of an anchor having a longitudinally slit inward end having an annular collar at the inward end intended to fit within a ledge or undercut portion of a hole. The anchor carries an expansion pin in a slightly withdrawn, central region of the anchor prior to expansion of the anchor. To expand the anchor, the expansion pin is pushed forwardly, toward the inward end of a hole, thereby causing expansion of the anchor on opposite sides of the longitudinal slit. The collar at the inward end of the anchor is intended to reside in the undercut or ledged portion of the hole, thereby securing the anchor.
In U.S. Pat. No. 3,815,694 granted June 11, 1974 to J. Giustino there is disclosed a tool for drilling a ledged hole in hard materials. The tool carries an internal blade which is pivoted outwardly as the tool is pressed into the hole. The patent shows that ledged holes are useful for holding toggle type fasteners.
While many of the anchors of the prior art, including those discussed above, are useful in concrete and wood, they are not particularly suitable for use in granite, with the possible exception of the patent to Schalge and Neos. This is because the prior art expanding anchors rely upon the softness or crumbling property of the material into which the anchor is inserted. For example, concrete is an aggregate material consisting of sand, rock and cement particles. Many prior art anchors are successful in cement because they displace or compress aggregate materials. However, this approach is not possible in hard materials such as granite. When a hole is drilled in such hard materials, the drilling process polishes the sidewalls of the hole. This is in contrast to concrete and similar materials which crumble on contact.
Accordingly, there is a need for an anchor which is especially suited to hard materials, such as granite.